Zucker–Hammett hypothesis

This hypothesis states that, if in an acid catalysed reaction, log 10 k 1 (first-order rate constant of the reaction) is linear in H0 (Hammett acidity function), water is not involved in the transition state of the rate-controlling step. However, if log 10 k 1 is linear in log 10 H + then water is involved. This has been shown to be incorrect by Hammett himself.
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1176 (https://doi.org/10.1351/pac199466051077)